The catalytic deuteration and tritiation of .DELTA..sup.3 -proline was reported by Robertson and Witkop, J. Am. Chem. Soc. 84, 1697 (1962). The procedure employed utilized Adams catalyst (platinum oxide) and produced labelled material in which considerable randomization of the deuterium and tritium labels was observed (Robertson and Witkop supra at 1700).
The incorporation of L- and DL- .DELTA..sup.3 -proline into peptides was described by McGee et al., Arch. Biochem. Biophys., 154, 483 (1973) and Felix et al., Int. J. Pept. Prot. Res., 5, 201 (1973).
Tritiated peptide compounds are articles of commerce. Thus, for example, tritiated thyrotropin releasing hormone (L-(Pyro)glu-L-His-L-2,3-.sup.3 H-Pro amide) is offered in catalog S (1973) of New England Nuclear. It is believed that this compound is prepared by (a) tritiation of D,L-2,3-dehydroproline, (b) resolution of the labelled enantiomers and (c) peptide synthesis and purification of labelled intermediates and product. The use of labelled compounds early in the synthesis with resulting loss of labelled material in part explains the high cost of the product.